The present invention relates generally to a heat transfer image-receiving sheet and, more particularly, to a heat transfer image-receiving sheet which enables high-quality images to be formed on both its sides.
Various heat transfer methods have been known so far in the art. Among them, there is proposed a method in which a heat transfer sheet prepared by carrying a sublimable dye, acting as a recording agent, on a substrate sheet such as a paper or a plastic sheet is used to form various full-color images on a heat transfer image-receiving sheet dyeable with the sublimable dye, for instance, that including a dye-receiving layer on the surface of paper or a plastic film.
According to this method, the thermal head of a printer is used as heating means to transfer a number of three- or four-color dots onto the heat transfer image-receiving sheet by a very quick heating stop, thereby reconstructing a full-color image of the original with the multi-color dots. The thus formed image is very clear because the coloring material used is a dye, and excels in the reproducibility and gradation of halftone because it excels in transparency. In addition, it is possible to obtain a high-quality image equivalent to that achieved by conventional offset or gravure printing and comparable to that attained by full-color photography.
Known as heat transfer image-receiving sheets usable with such a sublimation type of heat transfer technique as mentioned above are those made of such substrate sheets as plastic sheets, laminated sheets of plastic sheets with paper or the like, synthetic paper or plain paper, which have a dye-receiving layer or layers on one or both sides. Among them, an image-receiving sheet which enable images to be formed on both its sides by providing image-receiving layers on both sides of the substrate sheet is now expected to have wide applications in view of the effective exploitation of printing resources and a variety of image needs.
Some image-receiving sheets having image-receiving layers on both the sides have already been set forth in U.S. Pat. No. 4,778,782 and Japanese Patent Laid-Open (Kokai) Publication No. 64(1989)-47586.
However, the inventors have already found that the double-sided type of image-receiving sheet known so far in the art presents a problem inherent in images being formed on both its sides. For instance, when one image is formed on the first side of the sheet and another image is subsequently formed on the second side, not only is the image on the first side transferred onto the second side in the form of traces, but the image on the second side is left on the first side in the form of traces as well. As again found by the inventors, the cause of the "image traces" problem is unaccountable only by what is called the offset phenomenon or the transparency phenomenon ensuing from the thinness of the image-receiving sheet. Therefore, this "image traces" problem cannot drastically be solved, even though a substrate sheet having a hiding property well enough to prevent offset is used. Such image traces seriously degrade the commercial value of printed images.